The plant species Lycopersicon pennellii Corr. (also known as Solanum pennellii Corr.) inhabits the extremely dry, lower, western slopes of the Central Peruvian Andes. This species has a rather wide geographic distribution that extends from El Horador (Depto. Piura) in northern Peru to Camana (Depto. Arequipa) in southern Peru. The autecology of these native populations is such that often the only other vegetation growing in close proximity to Lycopersicon pennellii plants are cacti and bromeliads.
As a plant species, Lycopersicon pennellii is morphologically intermediate between potato and tomato. However, since Lycopersicon pennellii is interfertile in controlled pollinations with the cultivated tomato, it is commonly grouped with other wild species of tomato. Yu (1972) and Rick (1973) have shown that among tomato species, Lycopersicon pennellii leaves have a unique and special ability to withstand desiccation. They also point out that Lycopersicon pennellii distinguishes itself from other Lycopersicon species, except Lycopersicon chilense, in its ability to withstand conditions of extreme drought.
Both native, greenhouse and field populations of certain Lycopersicon pennellii have oily glands that produce a sticky exudate which covers the surfaces of Lycopersicon pennellii leaves, stems, peduncles, calyxes and fruits. An analysis of lipids in the leaves of Lycopersicon pennellii by Ermakov (1980) showed that the leaves have a high lipid content. The Ermakov study further showed that the Lycopersicon pennellii leaf lipids contain some 15 fatty acid components, the predominant ones being saturated fatty acids, especially capric acid (C10:0). In cultivated tomato leaves, e.g., the cultivar Gruntovy Gribovsky, Ermakov states that unsaturated fatty acids, especially linolenic acid (C18:3), usually prevail.
In addition to analyzing total leaf lipids, Ermakov also analyzed lipids isolated from the glandular hairs of Lycopersicon pennellii leaves. His results show that the glandular hair lipids are mainly polar and that they comprise over 70 percent of the total lipids in the leaves. In comparing the glandular hair lipids with well known plant galactolipids (for which a high concentration of unsaturated fatty acids is characteristic), Ermakov points out the glandular hair lipids have a high concentration of saturated fatty acids, especially those with a relative molecular size or length of up to C14.
Physical entrapment of arthropods by the exudate from glandular hairs of various plants is well known in wild Solanum species such as S. berthaultii, S. tarijense, and S. polyadenium. The exudate of the four-lobed (type A) trichomes, when exposed to atmospheric oxygen, forms a viscous substance which accumulates on the tarsi and mouthparts of green peach aphid, Myzus persicae Sulzer, the potato aphid, Macrosiphum Euphorbiae Thomas, and the potato leafhopper, Empoasca fabae Harris. The viscous material hardens and effectively immobilizes the insects, resulting in their death through starvation.
S. berthaultii also possesses a second type of glandular trichome (type B) which is slender and continuously secretes a sticky substance at its tip. This type of trichome has been found to be important in entrapping the two-spotted spider mite, Tetranychus urticae Koch, and tarsonemid mites; mites are not powerful enough to rupture the membrane of the fourlobed glandular trichomes. Utilizing an electronic feeding monitor, Lapointe and Tingey (1984) demonstrated that aphid feeding on S. berthaultii leaves was characterized by a delay in probing, a decrease in the duration of probes, and that an overall physical removal of the type B exudate resulted in a decrease of resistance as measured by these parameters.
The most abundant of the types of glandular hairs in the genus Lycopersicon are the type IV and VI trichomes. The type VI trichome is similar in appearance to the type A trichomes on Solanum species while the type IV trichome is similar to the type B of Solanum. Physical entrapment of the carmine spider mite, Tetranychus cinnabarinus Boisduval, the two-spotted spider mite, T. urticae, and the greenhouse whitefly, Trialeurodes vaporariorum Westwood by type IV glandular exudate appears to be the principal component of resistance to these pests by certain Lycopersicon species (Gentile et al., 1969, 1968). Removal of the exudate with alcohol resulted in successful oviposition and normal nymphal development of the greenhouse whitefly (Gentile et al., 1968). The release of a viscous exudate upon rupture of the type VI trichomes is suggested as the basis for physical entrapment of insects in several wild tomato species.
L. pennellii, especially accession LA716, is resistant to several insect species, including greenhouse whitefly, carmine and two-spotted spider mites, and potato and green peach aphids. Insect resistance in L. pennellii is largely attributed to the type IV glandular hairs, which are not present on the foliage of L. esculentum. Resistance to greenhouse whitefly has been attributed to the entrapment of adults in the sticky exudate of type IV trichomes (Gentile et al., 1968). Physical entrapment of carmine and two-spotted spider mites and potato aphids in exudate of type IV trichomes was also suggested as the mode of resistance to these pests (Gentile et al. 1969, Gentile and Stoner 1968b). Clayberg (1975) observed that a periclinal chimera, consisting of the epidermis, with dense indumentum of L. pennellii and a "core" of L. esculentum origin, had levels of whitefly resistance equal to that in L. pennellii but a reduced level of resistance to potato aphids.
The type IV trichome of L. pennellii, its hybrids and progeny are slender hairs with pointed tips about 0.2 to 0.4 mm in length, standing on a large simple basal cell. The hair is glandular and it continuously secretes a droplet which is not membrane-bound. Further details of these trichomes may be found in Luckwill (1943). The exudate of the type IV trichomes of L. pennellii, its hybrids and progeny is composed of a complex mixture of glucose triesters of saturated straight chain and branched fatty acids (C4 to C12) (Burke et al. 1987). The most abundant fatty acids found in L. pennellii glucose esters include 2-methylpropanoic, 8-methylnonanoic and n-decanoic acids, with 2-methylbutanoic, 3-methylbutanoic and n-dodecanoic acids being present in relatively minor amounts. The positions of esterification have all been found to be the 2, 3 and 4 positions.
The 2,3,4-tri-O-acylhexoses of this invention are known compounds being disclosed in U.S. Ser. No. 709,550 filed Mar. 8, 1985, the disclosure of which is incorporated by reference. The hexoses are disclosed therein to be useful in cosmetic and toiletry formulations for humans, as "low calorie" fat substitutes in food, and as evaporation suppressants, antitranspirants and antidesiccants.